2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright IBM Corporation, 2008
20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
22 * For detailed explanation of Read-Copy Update mechanism see -
25 #include <linux/moduleparam.h>
26 #include <linux/completion.h>
27 #include <linux/interrupt.h>
28 #include <linux/notifier.h>
29 #include <linux/rcupdate.h>
30 #include <linux/kernel.h>
31 #include <linux/module.h>
32 #include <linux/mutex.h>
33 #include <linux/sched.h>
34 #include <linux/types.h>
35 #include <linux/init.h>
36 #include <linux/time.h>
37 #include <linux/cpu.h>
39 /* Global control variables for rcupdate callback mechanism. */
41 struct rcu_head
*rcucblist
; /* List of pending callbacks (CBs). */
42 struct rcu_head
**donetail
; /* ->next pointer of last "done" CB. */
43 struct rcu_head
**curtail
; /* ->next pointer of last CB. */
46 /* Definition for rcupdate control block. */
47 static struct rcu_ctrlblk rcu_sched_ctrlblk
= {
48 .donetail
= &rcu_sched_ctrlblk
.rcucblist
,
49 .curtail
= &rcu_sched_ctrlblk
.rcucblist
,
52 static struct rcu_ctrlblk rcu_bh_ctrlblk
= {
53 .donetail
= &rcu_bh_ctrlblk
.rcucblist
,
54 .curtail
= &rcu_bh_ctrlblk
.rcucblist
,
57 #ifdef CONFIG_DEBUG_LOCK_ALLOC
58 int rcu_scheduler_active __read_mostly
;
59 EXPORT_SYMBOL_GPL(rcu_scheduler_active
);
60 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
62 /* Controls for rcu_cbs() kthread, replacing RCU_SOFTIRQ used previously. */
63 static struct task_struct
*rcu_cbs_task
;
64 static DECLARE_WAIT_QUEUE_HEAD(rcu_cbs_wq
);
65 static unsigned long have_rcu_cbs
;
66 static void invoke_rcu_cbs(void);
68 /* Forward declarations for rcutiny_plugin.h. */
69 static void rcu_process_callbacks(struct rcu_ctrlblk
*rcp
);
70 static int rcu_cbs(void *arg
);
71 static void __call_rcu(struct rcu_head
*head
,
72 void (*func
)(struct rcu_head
*rcu
),
73 struct rcu_ctrlblk
*rcp
);
75 #include "rcutiny_plugin.h"
79 static long rcu_dynticks_nesting
= 1;
82 * Enter dynticks-idle mode, which is an extended quiescent state
83 * if we have fully entered that mode (i.e., if the new value of
84 * dynticks_nesting is zero).
86 void rcu_enter_nohz(void)
88 if (--rcu_dynticks_nesting
== 0)
89 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
93 * Exit dynticks-idle mode, so that we are no longer in an extended
96 void rcu_exit_nohz(void)
98 rcu_dynticks_nesting
++;
101 #endif /* #ifdef CONFIG_NO_HZ */
104 * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
105 * Also disable irqs to avoid confusion due to interrupt handlers
106 * invoking call_rcu().
108 static int rcu_qsctr_help(struct rcu_ctrlblk
*rcp
)
112 local_irq_save(flags
);
113 if (rcp
->rcucblist
!= NULL
&&
114 rcp
->donetail
!= rcp
->curtail
) {
115 rcp
->donetail
= rcp
->curtail
;
116 local_irq_restore(flags
);
119 local_irq_restore(flags
);
125 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
126 * are at it, given that any rcu quiescent state is also an rcu_bh
127 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
129 void rcu_sched_qs(int cpu
)
131 if (rcu_qsctr_help(&rcu_sched_ctrlblk
) +
132 rcu_qsctr_help(&rcu_bh_ctrlblk
))
137 * Record an rcu_bh quiescent state.
139 void rcu_bh_qs(int cpu
)
141 if (rcu_qsctr_help(&rcu_bh_ctrlblk
))
146 * Check to see if the scheduling-clock interrupt came from an extended
147 * quiescent state, and, if so, tell RCU about it.
149 void rcu_check_callbacks(int cpu
, int user
)
154 hardirq_count() <= (1 << HARDIRQ_SHIFT
)))
156 else if (!in_softirq())
158 rcu_preempt_check_callbacks();
162 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
163 * whose grace period has elapsed.
165 static void rcu_process_callbacks(struct rcu_ctrlblk
*rcp
)
167 struct rcu_head
*next
, *list
;
170 /* If no RCU callbacks ready to invoke, just return. */
171 if (&rcp
->rcucblist
== rcp
->donetail
)
174 /* Move the ready-to-invoke callbacks to a local list. */
175 local_irq_save(flags
);
176 list
= rcp
->rcucblist
;
177 rcp
->rcucblist
= *rcp
->donetail
;
178 *rcp
->donetail
= NULL
;
179 if (rcp
->curtail
== rcp
->donetail
)
180 rcp
->curtail
= &rcp
->rcucblist
;
181 rcu_preempt_remove_callbacks(rcp
);
182 rcp
->donetail
= &rcp
->rcucblist
;
183 local_irq_restore(flags
);
185 /* Invoke the callbacks on the local list. */
189 debug_rcu_head_unqueue(list
);
198 * This kthread invokes RCU callbacks whose grace periods have
199 * elapsed. It is awakened as needed, and takes the place of the
200 * RCU_SOFTIRQ that was used previously for this purpose.
201 * This is a kthread, but it is never stopped, at least not until
202 * the system goes down.
204 static int rcu_cbs(void *arg
)
210 wait_event(rcu_cbs_wq
, have_rcu_cbs
!= 0);
211 local_irq_save(flags
);
214 local_irq_restore(flags
);
216 rcu_process_callbacks(&rcu_sched_ctrlblk
);
217 rcu_process_callbacks(&rcu_bh_ctrlblk
);
218 rcu_preempt_process_callbacks();
222 return 0; /* Not reached, but needed to shut gcc up. */
226 * Wake up rcu_cbs() to process callbacks now eligible for invocation.
228 static void invoke_rcu_cbs(void)
232 local_irq_save(flags
);
234 wake_up(&rcu_cbs_wq
);
235 local_irq_restore(flags
);
239 * Wait for a grace period to elapse. But it is illegal to invoke
240 * synchronize_sched() from within an RCU read-side critical section.
241 * Therefore, any legal call to synchronize_sched() is a quiescent
242 * state, and so on a UP system, synchronize_sched() need do nothing.
243 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
244 * benefits of doing might_sleep() to reduce latency.)
246 * Cool, huh? (Due to Josh Triplett.)
248 * But we want to make this a static inline later. The cond_resched()
249 * currently makes this problematic.
251 void synchronize_sched(void)
255 EXPORT_SYMBOL_GPL(synchronize_sched
);
258 * Helper function for call_rcu() and call_rcu_bh().
260 static void __call_rcu(struct rcu_head
*head
,
261 void (*func
)(struct rcu_head
*rcu
),
262 struct rcu_ctrlblk
*rcp
)
266 debug_rcu_head_queue(head
);
270 local_irq_save(flags
);
271 *rcp
->curtail
= head
;
272 rcp
->curtail
= &head
->next
;
273 local_irq_restore(flags
);
277 * Post an RCU callback to be invoked after the end of an RCU-sched grace
278 * period. But since we have but one CPU, that would be after any
281 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
283 __call_rcu(head
, func
, &rcu_sched_ctrlblk
);
285 EXPORT_SYMBOL_GPL(call_rcu_sched
);
288 * Post an RCU bottom-half callback to be invoked after any subsequent
291 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
293 __call_rcu(head
, func
, &rcu_bh_ctrlblk
);
295 EXPORT_SYMBOL_GPL(call_rcu_bh
);
297 void rcu_barrier_bh(void)
299 struct rcu_synchronize rcu
;
301 init_rcu_head_on_stack(&rcu
.head
);
302 init_completion(&rcu
.completion
);
303 /* Will wake me after RCU finished. */
304 call_rcu_bh(&rcu
.head
, wakeme_after_rcu
);
306 wait_for_completion(&rcu
.completion
);
307 destroy_rcu_head_on_stack(&rcu
.head
);
309 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
311 void rcu_barrier_sched(void)
313 struct rcu_synchronize rcu
;
315 init_rcu_head_on_stack(&rcu
.head
);
316 init_completion(&rcu
.completion
);
317 /* Will wake me after RCU finished. */
318 call_rcu_sched(&rcu
.head
, wakeme_after_rcu
);
320 wait_for_completion(&rcu
.completion
);
321 destroy_rcu_head_on_stack(&rcu
.head
);
323 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
326 * Spawn the kthread that invokes RCU callbacks.
328 static int __init
rcu_spawn_kthreads(void)
330 rcu_cbs_task
= kthread_run(rcu_cbs
, NULL
, "rcu_cbs");
333 early_initcall(rcu_spawn_kthreads
);